With evolution of a wireless local area network (WLAN) standard, a current IEEE (Institute of Electrical and Electronics Engineers) 802.11 working group starts to research and formulate a next-generation wireless fidelity (WiFi) standard. The next-generation WiFi standard is referred to as a high efficiency WLAN (HEW) for short, and a project code name is 802.11ax. The next-generation WiFi standard aims to increase a system capacity to more than 10 Gbps, and specially concerns an outdoor deployment scenario of WiFi devices and a high-density deployment scenario of WiFi devices.
For a high-density distribution scenario, a competitive access mechanism of conventional WiFi cannot work well due to low efficiency of the competitive access mechanism, and a new media access mechanism is in urgent need of introduction. Therefore, a multiuser transmission technology with an advantage of relatively high performance is very likely to be introduced into 11ax. Orthogonal frequency division multiple access (OFDMA) that includes uplink (UL) OFDMA and downlink (DL) OFDMA may be introduced into 11ax. In addition, uplink multi-user multiple-input multiple-output (UL MU MIMO) may also be introduced (DL MU MIMO has been introduced into 11ac). The 11ax should support all transmission modes supported by an existing standard. Actually, evolution of the WiFi standard always adheres to this idea, which is shown in Table 1.
TABLE 1StandardSupported transmission mode11a/gSU (single user)11nSU, SU MIMO11acSU, SU MIMO, DL MU MIMO11axSU, SU MIMO, DL MU MIMO, UL MU MIMO, UL/DLOFDMA
It may be seen from Table 1 that, an 11a/g standard supports a single user (SU) transmission mode, an 11n standard supports the SU transmission mode and an SU MIMO transmission mode, and an 11ac standard supports the SU transmission mode, the SU MIMO transmission mode, and a DL MU MIMO transmission mode. In the related field, each standard has a particular transmission frame structure. A field in a physical header of a transmission frame is used to indicate a frame structure of the transmission frame.
It may be seen from Table 1 that, a frame structure of the 11ax standard not only should support the newly-introduced UL/DL OFDMA and UL MU MIMO, but also should support the existing three transmission modes. In addition, the frame structure of the 11ax should also be identified by a HEW device and an existing device as early as possible. That is, the HEW device can identify the frame as an 11ax transmission frame according to a physical header of a transmission frame; or the existing device can determine, according to a physical header of a transmission frame, that the transmission frame is a transmission frame that cannot be understood by the existing device. Therefore, a frame structure of a transmission frame needs to be indicated in a physical header of the transmission frame.
It is found in practice that, in the related field, a particular frame structure is used in each standard, and a physical header of the frame structure can indicate only this frame structure. However, with development of a WLAN, more transmission modes need to be supported, and multiple frame structures may be designed in one standard. As a result, the solution in the related field cannot satisfy the needs of various applications. For example, the 11ax standard needs to support more than five transmission modes. It is difficult for one frame structure to satisfy this requirement, that is, at least two frame structures may need to be designed to separately support different transmission modes. Therefore, a method for indicating multiple different frame structures is in urgent need.